Despite an abundance of scientific evidence on quality-improving clinical and organizational practices, national performance on many quality measures remains poor. Prior research suggests this is because many health care organizations struggle to implement new practices, and ultimately fail to implement new practices. As a result, millions of patients suffer negative consequences, including higher mortality and morbidity. This research aims to increase the successful implementation of existing and future practices by advancing the evidence-base on how three aspects of organizational behavior contribute to the implementation success of new practices: implementation leaders' behaviors, workforce engagement, and use of learning activities. The specific aims are: (1) to characterize implementation leaders' behaviors, and to develop hypotheses about the relationship between their behaviors and implementation success; (2) to examine the relationships between workforce engagement (for different segments of the hospital workforce), implementation success, and clinical performance; and (3) to examine the impact of hospitals' use of various learning activities on implementation success and clinical performance. These aims emerge from a theoretically-derived model of the implementation process. The model posits that implementation leader behavior is associated with workforce engagement and with the use of learning activities intended to facilitate implementation. In turn, both workforce engagement and use of learning activities are associated with the implementation success of new practices, and clinical performance. To evaluate this model, and achieve the three aims, a mixed methods study - using quantitative and qualitative data from more than 700 hospitals participating in the D2B Alliance - will be conducted. The D2B Alliance is a national campaign to promote the implementation of evidence-based practices to improve door-to-balloon time (i.e., time between hospital arrival and balloon inflation during primary percutaneous coronary intervention (PCI)) for patients with ST-segment elevation myocardial infarction (STEMI), a common type of heart attack. The first aim will be achieved through qualitative analysis of interview data from a subsample of D2B Alliance hospitals. Aims 2 and 3 will be accomplished through multivariable linear regression analyses and structural equation modeling using data on workforce engagement, implementation of recommended practices, and use of learning activities from a web-based survey of D2B Alliance hospitals. Data on clinical performance, measured as the one-year percentage change in hospital patients with STEMI treated with PCI with door-to-balloon time within national guidelines, will be obtained from the Hospital Quality Alliance. In identifying specific strategies for improving organizations' implementation of new practices, this research aligns with national quality improvement priorities as many new practices relate to patient safety, prevention/care management, cost-effectiveness, and innovation dissemination.